The Dietary Index for Gut Microbiota (DI-GM) is a novel metric assessing diet quality in relation to gut microbial composition. However, its association with all-cause mortality (ACM) in coronary heart disease (CHD) patients remains unexplored. This study aimed to evaluate the association between DI-GM and ACM among the CHD population. This retrospective cohort study utilized 2005-2018 National Health and Nutrition Examination Survey data. DI-GM scores were calculated based on 24-hour dietary recall data. The association between DI-GM and ACM in CHD patients was assessed using weighted Cox proportional hazards models and restricted cubic spline analyses. Subgroup analyses and interaction tests were performed to examine the robustness of the findings and potential effect modifiers. A total of 1537 CHD patients were included, representing 81,24,166 US adults. The overall ACM rate was 37.41%. Higher DI-GM scores were significantly associated with lower ACM risk. Compared with participants with scores of 0 to 3, those with scores ≥6 and 5 had significantly reduced ACM risk, with hazard ratios of 0.593 (95% confidence interval: 0.413-0.851; P = .005) and 0.649 (95% confidence interval: 0.432-0.975; P = .037), corresponding to 40.7% and 35.1% reductions in ACM risk. Restricted cubic spline analysis revealed a nonlinear inverse association between DI-GM and ACM. Subgroup analyses indicated that diabetes status may modify this association (P for interaction = .046). Higher DI-GM scores were nonlinearly and inversely associated with ACM among CHD patients. This association may be modified by diabetes status.